1. Field of the Invention
This invention relates to a method and apparatus for recording and reading information, and an information recording element used in the same.
2. Description of the Prior Art
Recently, various types of optical recording elements have been greatly developed. Typical examples of such optical recording elements are of the write once type and the rewritable type. These optical recording elements have a disk comprising a recording medium (typically in the form of a recording thin film) for recording information. It has been proposed to use various substances as a material for a recording thin film, for example, alloys such as TeC, SeTe, and TeOGeInPb, magnetic alloys such as GdTbFe(Co), cyanines, and naphtoquinone organic dyes. These optical recording media record information with a principle based on the magneto-optic effect, photoisomerization, phase transformation effect, etc. Each type of these optical recording media has an advantage.
When information is recorded in an optical recording element of the phase transformation type, a light beam such as a laser beam is used to irradiate a recording film formed in the element to transfer the state of a material consisting the recording film, i.e., from crystal to amorphous. This process is described in U.S. Pat. No. 3,530,441 in the name of Energy Conversion Devices, Inc. As a recording film used in this process or similar process, a tellurium-tin-selenium film, a tellurium oxide film, and a selenium-indium-antimony film have been developed. When manufacturing an optical recording element of the phase-change type, a substrate on which a suitable material is deposited is heated, and thereafter gradually cooled so that the state of the material is transferred from amorphous to crystal. Hence, the manufacturing process of an optical recording element of this type requires a prolonged period of time and rather complicated procedures.
An optical recording element of the write once type has a recording film made of an alloy. Information is recorded in the form of a series of pits or grooves which are formed in the recording film by irridiation with a laser beam. Therefore, this process requires a large amount of energy when information is recorded.
In a rewritable optical recording element, which has been put into a practical use, information is recorded and read out using the photomagnetic effect. When information is read out from the rewritable optical recording element, changes in the polarizing angle of material in the recording film which are caused by the Kerr effect are detected by a suitable detecting means. Such a detecting means must detect the changes with very high precision and stability because the Kerr rotational angle of a material is very small (usually, smaller than 1 degree). However, materials showing a larger Kerr effect and also having a smaller coersive force have not yet been developed.